Building Materials - Bricks and Stones Complete Study Notes

Brick

Composition of Good Brick Earth

Following are the constituents of brick earth:

1. Alumina

It is the chief constituent of every kind of clay. Good brick earth should contain about 20 to 30 percent of alumina. This constituent imparts plasticity to earth so that it can be molded.

2. Silica

A good brick earth should contain about 50 to 60 percent silica. The presence of this constituent prevents cracking, shrinking, and warping of raw bricks. It thus imparts a uniform shape to the bricks.
Excess silica destroys the cohesion between particles, and bricks become brittle.

3. Lime

It should be present in a finely powdered state and not in a lump.
Lime prevents shrinkage of raw bricks. Sand alone is infusible. But it slightly fuses at kiln temperature in the presence of lime.
Excess lime causes the brick to melt, and hence, its shape is lost. Lumps of lime are converted into quick lime after burning, and this quick lime slakes and expands in the presence of moisture.

4. Oxide of Iron

About 5 to 5 percent is desirable in good brick earth. It helps lime to fuse sand. It also imparts red color to bricks.
Excess of oxide of iron makes the bricks dark blue or blackish

5. Magnesia

A small quantity of magnesia in brick earth imparts yellow tint color and decreases shrinkage. But excess magnesia leads to the decay of bricks.

Harmful Ingredients in Brick Earth

1. Lime

It causes unsoundness in the brick if present in excess amounts.

2. Iron pyrites

If iron pyrites are present in brick earth, bricks crystallize and disintegrate during burning.

3. Alkalies

These are mainly in the form of soda and potash

4. Pebbles

The presence of pebbles or grits of any kind is undesirable in brick earth because it will not allow the clay to be mixed uniformly and thoroughly, resulting in weak and porous bricks.

5. Organic Matter

Presence of organic matter in brick earth assists in burning. But if such matter is not completely burnt, bricks become porous.

Manufacture of bricks

1. Preparation of clay

Clay of bricks is prepared in the following order:

Unsoiling
Digging
Cleaning
Weathering
Blending
Tempering

2. Moulding

Hand Moulding

Machine Moulding

Plastic Clay Machine
Dry Clay Machine

3. Drying

4. Burning: Burning of bricks is done either in clamps or in kilns.

(a) Clamps: Its shape in the plan is generally trapezoidal. The clamp floor is prepared so that the short end is slightly in the excavation, and the wider end is raised at an angle of about 15° from ground level.

(b) Kilns: A kiln is large over to burn bricks. The kilns used in the manufacture of bricks are of the following two types.

(i) Intermittent kilns (ii) Continuous kilns

(i) Intermittent Kiln: This may be overground or underground. They are classified in two ways: (a) intermittent up-drought kilns, (b) Intermittent down-draught kilns

Comparison between bull's trench kiln and Hoffman's kiln

Comparison between clamp Burning and kiln Burning

Tests For Bricks

1. Absorption

A brick is taken, and it is weighted dry. It is then immersed in water for 16 hours.
Then weight again, and the difference in weight should not, in any case, exceed
(a) 20 percent of the weight of dry brick for first-class bricks.
(b) 22.5 percent for second-class bricks.
(c) Twenty-five percent for third-class bricks.

2. Crushing strength

Minimum crushing strength for first-class bricks and second class bricks

3. Hardness

In this test, a scratch is made on a brick surface with the help of a fingernail. If no impression is left on the surface, brick is treated sufficiently hard.

4. Presence of soluble salts

Soluble salts, if present in bricks, will cause efflorescence on the surface of bricks.
It is immersed in water for 24 hours. It is then taken out and allowed to dry in the shade. The absence of grey or white deposits on its surface indicates the absence of soluble salts.
If the white deposits cover about 10% surface, the efflorescence is slight.
When white deposits cover about 50% of the surface thin, it is moderate.
If grey or white deposits are found on more than 50% of the surface, the efflorescence becomes heavy and is treated as serious.

5. Shape and Size

Its shape should be truly rectangular with sharp edges.
20 bricks are randomly selected of standard (19 × 9 × 9 cm) for good quality bricks, the results should be within the following permissible limits:
Length – 368 cm to 392 cm
Width – 174 cm to 186 cm
Height – 174 to 186 cm

6. Soundness

In this test, two bricks are taken, and they are stuck with each other.
Bricks should not break, and a clear ringing sound should be produced.

7. Structure

It should be homogenous, compact, and free from defects such as holes, lumps, etc.
High duty fire-clays can resist temperature range of 1482°C to 1648°C; medium-duty fire-clays can resist temperature range of 1315°C to 1482°C, and low duty fire-clays can resist temperature up to 870°C only.

Quality of Good Bricks

The bricks should be table-molded, well burnt in kilns, copper-colored free from cracks, and sharp and square edges.
The bricks should be uniform in shape and standard size.
The bricks should give a clear metallic ringing sound when struck with each other.
The bricks, when broken or fractured, should show a bright, homogeneous, uniform, compact structure free from voids.
The brick should be sufficiently hard. No impression should be left on the brick surface when scratched with finger hail.
The bricks should not break into pieces when dropped flat on the hard ground from a height of about one meter.
The bricks, when soaked in water for 24 hours, should not show deposits of white salts when allowed to dry in the shade.
No brick should have a crushing strength below 5.50 N/MM².

Classification of Bricks

The bricks can broadly be divided into two categories:

1. Unburnt Bricks: The unburnt or sun-dried bricks are dried with the help of heat received from the sun after the process of molding. These bricks can only be used to construct temporary and cheap structures. Such bricks should not be used at places exposed to heavy rains.

2. Burnt Bricks: These are classified into four categories:

First Class Bricks
- These bricks are table-molded and of standard shape, burnt in kilns.
- The surfaces and edges of the bricks are sharp, square smooth, and straight.
- First-class bricks have all qualities of good bricks.
- These bricks are used for superior work of permanent nature.
Second Class Bricks
- These bricks are ground molded, and they are burnt in kilns.
- The surface of these bricks is somewhat rough, and the shape is also slightly irregular.
- These bricks are commonly used at places where bricks work is to be provided with a coat of plaster.
Third Class Bricks
- These are ground molded, and they are burnt in clamps.
- These bricks are not hard, and they have a rougsurfacesce with irregular and distorted edges.
- These bricks give a dull sound when struck together.
- They are used for unimportant and temporary structures.

Size and Weight Of Bricks(For India)

Standard size of bricks is 19 cm × 9 cm × 9 cm
Normal size (with mortar) is 20 cm × 10 × 10 cm.
The commonly adopted nominal size of traditional bricks is 23 cm × 11.4 cm × 7.6 cm.
It is found that the weight of 1 m³ of bricks earth is about 1800 kg. Hence the average weight of a brick will be about 3 to 3.50 kg.

Shape of Bricks

1. Bulinose Brick

A brick molded with a rounded angle is a bulbullnoset used for a rounded quoin.
A connection formed when a wall takes a turn is known as quoin.

2. Channel Bricks

These bricks are molded to the shape of a gutter or a channel, and they are very often glazed.
These bricks are used to function as drains.

3. Coping bricks

These bricks are made to suit the thickness of walls on which coping is provided.
Such bricks take various forms, such as chamfered half-round or saddle-back.

4. Cownose Bricks

A brick molded with a double bullnose on end is a cow nose.

5. Curved Sector Bricks

These bricks are in the form of a curved sector, and they are used in the construction of circular brick masonry pillars brick chimneys.
The perforation may be circular, square, rectangular, or any other regular shape in cross-section.
The water absorption after immersion for 24 hours should not exceed 15% by water.
Compressive strength of perforated bricks should not be less than 7 N/mm² on the gross area.

6. Hollow Bricks

These are also known as cellular or cavity bricks. Such bricks have a wall thickness of about 20 mm to 25 mm. They are prepared from special homogeneous clay. They are light in weight, about one-third of the ordinary bricks of the same size. The use of such bricks leads to speedy construction. They also reduce the transmission of heat, sound, and dampness. They are used in the construction of brick partitioning.

7. Paving bricks

These bricks are prepared from clay containing a higher percentage of iron. Excess iron vitrifies the bricks at a low temperature. Such bricks resist better the abrasive action of traffic. Paving bricks may be plain or checkered.

8. Perforated Bricks

Perforated bricks are used to construct brick panels for lightweight structures and multi-storeyed framed structures.

STONES

1. GENERAL CLASSIFICATION OF STONES

The building stones are obtained from rocks classified in the following three ways.

Geological classification
Physical classification
Chemical classification

1.1. Geological classification

(i) Igneous rocks are formed by the cooling of molten magma

Example:- Plutonic rocks – Granite

Hypabyssal rocks – dolerite

Volcanic rocks – Basalt

(ii) Sedimentary rocks are formed by the deposition of weathering products on pre-existing rocks. Residual, sedimentary, chemical and organic deposits are sedimentary deposits.

Example:- Gravel, sandstone, limestone, gypsum, etc

(iii) Metamorphic rocks are formed by the change in character in pre-existing rocks.

Example:- quartzite anthracite.

1.2. Physical classification

Based on the general structure of the rock.

(i) Stratified rocks:- They possess a plane of stratification. The sedimentary rocks are distinctly stratified.

(ii) Unstratified rocks:- The structure may be crystalline granular or compact granular.

(iii) Foliated Rocks:– It is a common cause of metamorphic rocks.

1.3. Chemical classification

(i) Siliceous Rocks- Silica Predominates.

Example:- Granite, Quartzites

(ii) Argillaceous Rocks- Argil or clay predominates

Example:- Slates, laterites

(iii) Calcareous Rocks- Carbon Predominates.

Example:- Limestone, Marble.

2. TESTS FOR STONE

2.1. Acid Test

In the test, a sample of stone weighing about 0.5N to 1N is taken and placed in a solution of hypo chloric acid with one percent strength for seven days. The solution is agitated at intervals. A good building stone maintains its sharp edges.

2.2. Attrition test

The test is conducted to determine the wear of stones used in road construction. The test results indicate the resisting power of stones against grinding action under traffic.

2.3. Crushing Test

The compressive strength of the stone is found out with the test. The sample of stone cut into cubes 40mm × 40mm × 40mm are used.

2.4. Crystallization Test

In this test, four cubes of side 40mm are taken and dried for 72 hours and weighed. They are then 14% solution of Na₂SO₄ for 2 hrs and dried at 100°C. The difference in weight is noted, and each time difference is noted in at least 5 samples.

2.5. Freezing and thawing test

The stone specimen is kept immersed in water for 24 hours and placed at a freezing temperature of —12ºC for 24 hours. It is then thawed or warmed at atmospheric temperature.

2.6. Hardness Test

A cylinder of diameter 25 mm and height 25 mm is taken and weighed. It is placed in Dorry’s testing machine and pressed at a pressure of 12.5 N. The machine's disc is rotated at a speed of 28 rpm. During the rotation of the disc, the coarse sand of standard specification is sprinkled on top of the disc. After 1000 revolutions, the specimen is taken and weighed.

2.7. Microscopic Test

In this test, a sample of stone is subjected to microscopic examination for various properties such as average grain size, pores, fissures, mineral constituents, and texture of stone.

3. QUALITIES OF GOOD BUILDING STONE

(i) For a good structural stone, the crushing strength should be greater than 100 N/mm².

(ii) The stones to be used for work should be decent in appearance and be capable of preserving their color for a long time.

(iii) A good building stone should be durable.

(iv) The stones should be such that they can be easily conserved, molded, cut, and dressed.

(v) For a good building stone, its fracture should be sharp, even bright, and clear with grains.

(vi) The coefficient of hardness worked out in the hardness test should be greater than π to be used in road work.

(vii) If the wear in the attrition test is more than 3 percent, the stone is not satisfactory.

(viii) For a good building stone, its specific gravity should be greater than 2.7 or so

(ix) All stones are more or less porous; percentage absorption by weight after 24 hours should not exceed 0.6

(x) A good building stone should have a compact fine cry stalling structure free from patches.

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